1. Field of the Invention
This invention relates generally to an apparatus and method for facilitating circuit board processing and, more specifically, to a reusable circuit board carrier and method of using same that allows circuit boards to be processed on conventional semiconductor device assembly equipment commonly employed with lead frames.
2. State of the Art
The manufacture of packaged semiconductor devices is a most competitive, high volume industry. Because of its voluminous production nature, even minute improvements in manufacturing efficiency and/or quality can make a considerable difference in overall manufacturing costs when accumulated over hundreds of thousands or even millions of units. Thus, automation of every manufacturing process is essential for one in the industry to compete, and improving those automated processes to make them more efficient and produce fewer defects is necessary to stay competitive.
Automation requires large capital expenditures in automated manufacturing and processing equipment. Moreover, such automated equipment is typically configured to process a specific component or component type having a particular standardized configuration, usually to the exclusion of other types of components. For example, dedicated equipment is purchased for fabrication of packaged semiconductor devices wherein a semiconductor die is mounted to a lead frame, wire-bonded thereto, encapsulated by transfer molding and then trimmed and formed to remove mold flashing and extraneous lead frame strip elements and form the external ends of the lead frame leads. Adaptability of at least some of such equipment, however, to accommodate another type of assembly, such as a printed circuit board assembly, would increase the value of the capital investment by providing greater opportunity for use and manufacturing flexibility.
One way to increase efficiency in the manufacturing of semiconductor devices is to process the devices in batches. Batch processing allows a group of components to be indexed through a given process station in greater numbers compared to throughputting single components, and results in more efficient utilization of the processing equipment. Thus, processing equipment is typically configured to perform one or more operations on a number of devices in a single cycle, creating faster processing cycle times and a lower cost per unit.
In order to accommodate batch processing in the manufacturing of packaged semiconductor devices, it is known in the art to form several similar components together as a unit for processing. For example, lead frames are typically formed as a linear lead frame strip comprised of several lead frames joined together at their peripheries. Thus, all of the lead frames in a lead frame strip can be substantially simultaneously processed by the addition of dice, subsequent wire bonding, and finally encapsulation to form several packaged semiconductor devices, which are separated in a final trim and form operation, as previously described.
Lead frame strips commonly employ relatively robust longitudinal rail segments along each edge to stiffen the strip and provide indexing holes for manipulation of the strip within and between processing stations. Lead frames may also be provided with a carrier that not only provides structural support for the lead frame strip during processing, but is adapted to be indexable and/or conveyable by the manufacturing equipment. For example, in U.S. Pat. No. 5,111,935, a universal lead frame carrier is disclosed to hold individual strips of lead frames together with their respective chips for bonding. The lead frame carrier can then be used to systematically move the lead frame from station to station during manufacture. U.S. Pat. 4,554,404 discloses another lead frame support. Magazines, such as disclosed in U.S. Pat. No. 4,910,886, may be employed to transport or store a large number of lead frame strips, with or without carriers.
Because of the advantages of batch processing and workpiece handling techniques employed in the manufacture of packaged semiconductor devices and, more particularly, to the processing of lead frame-based devices, such processing would also be beneficial in the manufacture of devices using printed circuit boards or other conductive trace-carrying substrates to which semiconductor dice are mounted and electrically connected. Conventional equipment used in the processing of packaged semiconductor devices, however, is typically configured to accommodate lead frame strips and/or packaged semiconductor devices based upon lead frames and is, therefore, not employable in the manufacture of printed circuit board assemblies and the like. Such equipment used in the manufacture of lead frame-based semiconductor devices (e.g., die attachers, wire bonders, drop dispensers and various lead frame magazines) would, however, be useful for the processing of printed circuit boards and other planar die supports, such as ceramic substrates, if a means could be formed to do so. Moreover, utilization of assembly equipment for more than one type of product would significantly reduce capital expenditures necessary for semiconductor manufacturing of different types of assemblies.
Different approaches have been employed for handling printed circuit boards, as disclosed in U.S. Pat. Nos. 3,915,307; 3,930,644; 4,109,379; 4,155,447; 4,198,024; 4,291,867; 4,385,781; 4,600,231; 4,763,782; 4,953,061; 5,339,221; 5,406,455; and 5,456,402. However, the foregoing patents are largely directed toward storage or transport of boards, in most instances are directed toward boards of substantial size, such as mother boards, are intended for installation of boards in chassis or other higher-level packaging for operational purposes, or are not adaptable to automated handling on a high-volume basis.
U.S. Pat. No. 5,044,615 discloses a printed circuit board holder adapted to retain a plurality of boards with a cam-type mechanism interposed between boards located in laterally and longitudinally adjacent recesses in the holder. The holder is not suitable in size or configuration for use with lead frame assembly processing and transport equipment, and may not provide the close locational tolerances necessary for use of die-attach and wirebonding equipment.
Thus, it would be advantageous to provide a reusable circuit board carrier and method of using same that allows circuit boards to be processed on conventional lead frame-based semiconductor device assembly equipment.
According to the present invention, a reusable circuit board carrier and method of using same is provided to allow circuit boards to be processed on conventional lead frame-based semiconductor device assembly equipment. More specifically, the circuit board carrier provides structure for temporarily aligning and securing a circuit board thereto for handling, storage and processing and allows the circuit board to be removed and replaced by another circuit board after processing has been completed. Moreover, the circuit board carrier may accommodate one or more circuit boards simultaneously in the same manner that multiple lead frames are manipulated together as a lead frame strip.
In a preferred embodiment, the circuit board carrier is comprised of an elongate, substantially planar member having a relatively thin cross-section and a generally rectangular perimeter. The circuit board carrier includes one or more board abutment surfaces for aligning at least one circuit board relative to the carrier, as well as structure for immobilizing and holding the aligned circuit board relative to the carrier. The abutment surfaces may include protrusions extending from the attachment surface of the circuit board carrier, the protrusions having various configurations for abutting flat or contoured edge surfaces of the circuit board. In addition, the immobilizing structure may include protrusions that extend from the attachment surface over a portion of the attached circuit board, or capture pins that fit through apertures in the circuit board and the attachment surface to pin the board to the carrier. Biased abutment surfaces that retract to allow insertion of a circuit board onto the carrier and then return to their original position once the circuit board is inserted may also be incorporated.
The carrier of the invention is sized and shaped to be transported between and processed on conventional semiconductor device assembly equipment and may include longitudinally extending lateral flanges along its outer edges. In addition, one or both of these flanges may include indexing holes formed therein to be engaged by transport and indexing devices. The carrier may also include an isolation member comprised of a relatively thin, substantially rectangular sheet of material, such as a static dissipative material or other suitable material known in the art, to isolate the circuit board from the carrier.
In another preferred embodiment, the circuit board carrier is comprised of two substantially parallel, elongate rails, each having grooves formed therein for holding one or more circuit boards. The circuit board carrier is provided with structure to keep the circuit board or boards from sliding out of the grooves, such as a transverse member having an interference fit with the grooves or otherwise secured to the rails (pin, screw, snap-fit, etc.) or a pivotally mounted member securable at its free end to the opposite rail. The circuit board carrier is sized and shaped to present circuit boards to be processed on conventional lead frame-based semiconductor device assembly equipment and may include indexing holes along the outer edge of one or both elongate rails to accommodate typical indexing equipment. The circuit board carrier includes at least one cross-member for connecting the two rails together, which may be positioned at an end of the rails to accommodate one or more circuit boards slid into the carrier, or proximate a medial portion of the rails so that one or more circuit boards may be carried on either side of the cross-member.
As used in the description of the present invention and specifically in the claims appended hereto, the term xe2x80x9ccircuit boardxe2x80x9d is not limited to particular structures such as conventional FR4 boards, but encompasses any conductor-carrying, substantially planar substrate or other die support member formed of any suitable material including, without limitation, conductor-carrying laminates formed of various materials, silicon or glass substrates with deposited (as by photolithography) conductors, ceramic substrates and other suitable conductor carriers as known in the art. Further, the term circuit board includes and encompasses all types of single- and multi-die assemblies, such as multi-chip modules (MCMs), including different types of dice or the same die type, the latter being exemplified by single in-line memory modules (SIMMs) or dual in-line memory modules (DIMMs).